Alan

First find the prime factors

nbr.           Prime factors

650.          2.5².13

680.          2³.5.17

760.          2³.5.19

The factors common to all three are 2 and 5, so the weight of each piece should be 2*5 → 10 lbs

The number of ways of choosing 4 from 6 is ncr(6,4) → 6!/(4!*2!) → 15

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Use the cosine rule:  

cos(A) = (b² + c² - a²)/(2bc)

eg cos(A) = (10² + 7² - 6²)/(2*10*7) → 0.8071

A = cos^-1(0.8071) → 36.2º

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Use the calculator on the home page here - it gives sqrt(10)*sqrt(10) = 10

All calculators work to a limited numerical precision though, so you can't rely on all floating point calculations to provide exact answers.

Total when paying monthly: €(205.22 + 11*175.95) → €2140.67

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See my corrected reply at http://web2.0calc.com/questions/need-asap_1#r3

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You are right - my answer above is incorrect!

Further thought suggests that it should be:

p(at least 1 boy and 1 girl) = 1 - (number of ways of choosing 4 boys from 10  +  number of ways of choosing 4 girls from 10)/number of ways of choosing 4 people from 20)

or:

p(at least 1 boy and 1 girl) = 1 - 2*nCr(10,4)/nCr(20,4) → 295/323 → 0.913

A and B means those items that are in both A and B at the same time.

Mutually exclusive means if an item is in A it cannot be in B, and if an item is in B it cannot be in A.

So, if A and B are mutually exclusive there are no items that occur in both A and B.  

In other words p(A and B) = 0

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I can only see 14 items that are greater than or equal to 98000 Omi.  This gives a probability of 14/20 = 0.7. (Or 70%)

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The same approach works for (b):

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